A vertical tapered sprue of 16 cms length is, kept full during pouring. To just avoid any aspiration, the cross-sectional areas at the centre and the bottom of the sprue must be in the ratio of

A. Build up of clay and other organic coatings on the molding sand particles B. Presence of foreign and scrap matter like iron particles, feyalite, etc. C. Occurrence of pieces of oil sand D. All of these

A. finish allowance B. contraction allowance C. taper allowance D. camber allowance

A. 70% sand and 30% clay B. 40% sand and 60% clay C. 30% sand and 70% clay D. 60% sand and 40% clay

A. Rough surface B. Blow holes C. hot tears D. Drop